Method for making ZSM-5 zeolites

ABSTRACT

The invention includes a method for preparing a crystalline zeolite having the X-ray diffraction lines of Table 1. The method includes preparing a template-free reaction mixture including at least one active source of a first oxide selected from the group consisting of an oxide of silicon, germanium or both, optionally at least one active source of a second oxide selected from the group consisting of an oxide of aluminum, boron, gallium, iron or a mixture thereof; and heating the reaction mixture at crystallization conditions for sufficient time to form a crystallized material containing zeolite crystals having the X-ray diffraction lines of Table 1, where said zeolite crystals have a first oxide/second oxide molar ratio greater than 12.

I. FIELD OF THE INVENTION

The present invention relates to a process for making crystallinezeolites.

II. BACKGROUND OF THE INVENTION

A. Introduction

Molecular sieves are a commercially important class of crystallinematerials. They have distinct crystal structures with ordered porestructures which are demonstrated by distinct X-ray diffractionpatterns. The crystal structure defines cavities and pores which arecharacteristic of the different species. Natural and syntheticcrystalline molecular sieves are useful as catalysts and adsorbents. Theadsorptive and catalytic properties of each molecular sieve aredetermined in part by the dimensions of its pores and cavities. Thus,the utility of a particular molecular sieve in a particular applicationdepends at least partly on its crystal structure. Because of theirunique sieving characteristics, as well as their catalytic properties,molecular sieves are especially useful in such applications as gasdrying and separation and hydrocarbon conversion. The term “molecularsieve” refers to a material prepared according to the present inventionas a fixed, open-network structure, usually crystalline, that may beused to separate hydrocarbons or other mixtures by selective occlusionof one or more of the constituents, or may be used as a catalyst in acatalytic conversion process.

B. Problems with Use of Templates

Prior art methods of preparing crystalline zeolites require astructure-directing agent or template (see, e.g., U.S. Pat. Nos.4,076,842; 4,296,083 and 4,490,342, regarding Zeolite ZSM-23 and U.S.Pat. No. 5,053,373, regarding Zeolite SSZ-32). Such templates add to theexpense and complexity of the process. Templates are typicallyrelatively expensive organic compounds and thus increase the expense ofreactants for the process. After crystallization of the zeolites, it isnecessary to remove the templates from the interior of the crystalssince they would otherwise block the pores. This is accomplished byheating and thus adds additional processing complexity and expense tothe process. There are also environmental risks associated with the useof the organic templates.

C. Problems with Excess Water in Reaction Mixtures

Prior art methods of preparing crystalline zeolites typically producefinely divided crystals which must be separated from an excess of liquidin which the zeolite is crystallized. The liquid, in turn, must betreated for reuse or else be discarded, with potentially deleteriousenvironmental consequences. Preparing commercially useful catalyticmaterials which contain the powdered zeolite also normally requiresadditional binding and forming steps. Typically, the zeolite powder ascrystallized must be mixed with a binder material and then formed intoshaped particles or agglomerates, using methods such as extruding,agglomeration, spray drying, and the like. These binding and formingsteps greatly increase the complexity of catalyst manufacture involvingzeolitic materials. The additional steps may also have an adverse effecton the catalytic performance of the zeolite so bound and formed.

D. Known Methods for Zeolites Having a Molar SiO₂/Al₂O₃ Ratio Below 12

Prior art methods of preparing crystalline zeolites typically producefinely divided crystals which must be separated from an excess of liquidin which the zeolite is crystallized. The liquid, in turn, must betreated for reuse or else be discarded, with potentially deleteriousenvironmental consequences. Preparing commercially useful catalyticmaterials which contain the powdered zeolite also normally requiresadditional binding and forming steps. Typically, the zeolite powder ascrystallized must be mixed with a binder material and then formed intoshaped particles or agglomerates, using methods such as extruding,agglomeration, spray drying, and the like. These binding and formingsteps greatly increase the complexity of catalyst manufacture involvingzeolitic materials. The additional steps may also have an adverse effecton the catalytic performance of the zeolite so bound and formed.

Crystalline zeolites may be divided into two general types based oncrystal structure considerations. One type includes zeolites having aSiO₂/Al₂O₃ molar ratio in the crystalline lattice typically less than12, which are conventionally prepared without an organic templatingagent. Many of these zeolites also contain sodalite substructures, andhave a tetrahedral atom density of less than about 15 TO₂/1000[Angstrom]³. Zeolites having these general characteristics include, forexample, zeolites A, N-A, ZK-4, faujasite, X, Y, ZK-5 and rho.

A number of processes have been offered for preparing crystallinezeolites of this type within discrete particles. For example, Howell etal., in U.S. Pat. No. 3,119,660, teaches a method for producingcrystalline metal aluminosilicate zeolite by reacting preformed bodiesof clay particles in an aqueous reactant mixture including alkali metaloxide. Similar processes for preparing zeolites from formed bodies,which may contain zeolitic seed crystals, in alkali solutions are alsotaught in U.S. Pat. No. 4,424,144 to Pryor et al.; U.S. Pat. No.4,235,753 to Brown et al.; U.S. Pat. No. 3,777,006 to Rundell et al.;U.S. Pat. No. 3,119,659 to Taggart et al.; U.S. Pat. No. 3,773,690 toHeinze et al.; U.S. Pat. No. 4,977,120 to Sakurada et al.; and GB 2 160517 A. U.S. Pat. No. 3,094,383 teaches a method of forming an A typezeolite by aging a homogeneous reaction mixture out of contact with anexternal aqueous liquid phase but under conditions to prevent thedehydration of the mixture. GB 1 567 856 discloses a method of preparingzeolite A by heating an extruded mixture of metakaolin powder and sodiumhydroxide.

In U.S. Pat. No. 4,058,586, Chi et al. disclose a method forcrystallizing zeolites within formed particles containing added powderedzeolite, where the formed particles furnish all of the liquid needed forcrystallization. Crystallizing the particles in an aqueous alkalinesolution is not required using the process of Chi et al.

Verduijn, in WO 92/12928, teaches a method of preparing binder-freezeolite aggregates by aging silica-bound extruded zeolites in an aqueousionic solution containing hydroxy ions. According to the disclosure ofVerduijn, the presence of zeolite crystals in the extrudate is criticalfor making strong crystalline zeolite extrudates. Verduijn et al., inEPO A1/0,284,206, describe a method of preparing binderless zeolite L byforming silica and preferably 10-50 wt. % preformed zeolite Lcrystallites into particles, and then reacting the particles with analkaline solution containing a source of alumina to form the zeolite L.

E. Known Methods for Zeolites Having a Molar SiO₂/Al₂O₃ Ratio Above 12

More recently, similar methods have been proposed for preparing highsilica zeolitic materials. Conventional methods for preparing highsilica materials, having a SiO₂/Al₂O₃ molar ratio of greater than about10, and more typically greater than about 20, typically involvescrystallizing the zeolites from aqueous solution. For example, U.S. Pat.No. 3,702,886 to Argauer et al. teaches a method of preparing ZSM-5 froma solution containing tetrapropyl ammonium hydroxide, sodium oxide, anoxide of aluminum or gallium, an oxide of silica or germanium, andwater. The digestion of the gel particles is carried out until crystalsform. The crystals are separated from the liquid and recovered.

A variation of the preparation procedure involves using clay as a sourceof alumina in preparing high silica zeolites. For example, U.S. Pat. No.4,091,007 discloses a method for preparing a crystalline aluminosilicatezeolite, specifically ZSM-4 or ZSM-5,from a reaction mixture where atleast about 70 weight percent of the alumina is provided by analumina-containing clay added to the reaction mixture. EPO A2/0,156,595discloses the preparation of crystalline zeolites having a silica toalumina mole ratio greater than 12 and a Constraint Index of 1 to 12 byforming a mixture of seed crystals, a source of silica, a source ofalumina and water into shaped particles, which are then crystallized inan aqueous reaction mixture containing a source of alkali cations. It isalso taught that alumina-containing clay may be used as an aluminasource. U.S. Pat. No. 4,522,705 is directed to a catalytic crackingcatalyst comprising an additive prepared by the in-situ crystallizationof a clay aggregate disclosed in EPO A2/0,156,595. U.S. Pat. No.5,145,659 teaches methods for increasing the silica content of a zeolitesupported on a matrix, where the matrix may be a clay.

Special methods for preparing the reaction mixture from which a zeolitemay be crystallized have also been proposed. In U.S. Pat. No. 4,560,542,a dried hydrogel containing silica and alumina is contacted with a fluidmedium containing an organic templating agent and maintained atspecified crystallization conditions to form a crystallinealuminosilicate.

In U.S. Pat. No. 5,240,892, a reaction mixture containing at least about30 weight percent solids content of alumina and precipitated silica istaught for preparing zeolites. The method of preparing the reactionmixture allows agitation of the mixture during crystallization, in spiteof the high solids content of the mixture.

Zeolite crystallization from reaction mixtures initially containing agel-like phase in equilibrium with an excess of liquid phase isdisclosed in R. Aiello et al., “Zeolite Crystallization from DenseSystems”, Materials Engineering 1992, Vol. 3, n. 3, pp. 407-416.

Other approaches to synthesis of crystalline zeolites have includedpreparing the zeolites in an essentially aqueous-free environment. Thesenon-aqueous methods have been described, for example, in ZEOLITES, 1992,Vol. 12, Apr./May, p. 343; ZEOLITES 1990, Vol. 10, Nov./Dec., p. 753;ZEOLITES 1989, Vol. 9, November, p. 468; Nature, Vol. 317(12), September1985, p. 157; and J. Chem. Soc., Chem. Commun., 1988, p. 1486. J. Chem.Soc., Chem. Commun., 1993, p. 659, describes a kneading method forsynthesizing ZSM-35 in a non-aqueous system, in which the amount ofliquids used to prepare a crystallization mixture is not sufficient towet all the solid particles so that the conglomerate reactant isactually a mixture of dry powder and small doughy lumps.

F. U.S. Pat. No. 5,558,851

A method is disclosed in U.S. Pat. No. 5,558,851 (the '851 patent) forpreparing a crystalline aluminosilicate zeolite from a reaction mixturecontaining only sufficient water so that the reaction mixture may beshaped if desired. In the method, the reaction mixture is heated atcrystallization conditions and in the absence of an external liquidphase, so that excess liquid need not be removed from the crystallizedmaterial prior to drying the crystals. For zeolites having a SiO₂/Al₂O₃molar ratio in the crystalline lattice greater than 12, there is noteaching of a method which does not require a template in the reactionmixture. Thus, the method of the '851 patent has the benefit of noexternal liquid phase to recycle or dispose, but still has therequirement for a template which can add greatly to the manufacturingexpense of raw materials.

G. Zeolite ZSM-5

Zeolite ZSM-5 is a zeolite having a SiO₂/Al₂O₃ molar ratio in thecrystalline lattice greater than 12, e.g., 20-5000. This zeolite is veryuseful in various hydrocarbon conversion processes, including dewaxingprocesses for lube oils. Zeolite ZSM-5 and the conventional preparationthereof are described in U.S. Pat. No. 3,702,886 (the '886 patent) andU.S. Pat. No. 3,770,614; and the disclosure of which, and particularlythe methods of preparation and the templating agents used in thepreparation, are incorporated herein by reference. The '886 patentteaches that a reaction mixture from which ZSM-5 can be suitablyprepared is formed by mixing sources of silica and alumina with atemplating agent, preferably tetrapropylammonium hydroxide, and sourcesof an alkali metal oxide, preferably sodium oxide. The teaching in the'851 patent for preparing a crystalline aluminosilicate zeolite from areaction mixture containing only sufficient water so that the reactionmixture may be shaped if desired includes applying that method toZeolite ZSM-5. However, for ZSM-5, there is no teaching of a methodwhich does not require a template in the reaction mixture. Thus, forZSM-5, the method of the '851 patent has the benefit of no externalliquid phase to recycle or dispose, but still has the requirement for atemplate.

H. Deficiencies in Known Processes for Making ZSM-5

Some of the methods described above reduce the number of steps incrystallizing zeolites. However, for zeolites having a SiO₂/Al₂O₃ molarratio in the crystalline lattice greater that 12, especially ZSM-5, noneof the cited patents provide a crystallization method combining atemplate-free reaction mixture with the ease of forming raw materialsand a minimum of water into shaped particles, and crystallizing thezeolites within the shaped particles while eliminating an externalliquid crystallization phase.

It would be advantageous to have a template-free, and thus relativelyinexpensive, process for producing ZSM-5 crystalline zeolites notrequiring an external liquid phase. This would greatly and beneficiallyreduce the cost of making such zeolites since such an external liquidphase is environmentally hazardous and must be treated or disposed ofafter the crystallization is complete. The method and process of theinstant invention provides such a process for making ZSM-5.

III. SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amethod for preparing crystalline zeolites having the X-ray diffractionlines of Table 1 of this specification without a template and using aminimum of liquid for crystallization.

It is further an object of one embodiment of the present invention toprovide a method for preparing crystalline zeolites having the X-raydiffraction lines of Table 1 of this specification in the form of shapedparticles.

It is a further object of one embodiment of the invention to provide amethod for preparing crystalline zeolites having the X-ray diffractionlines of Table 1 of this specification while minimizing an aqueous wastestream.

It is a further object of the invention to provide a method forpreparing zeolites having the X-ray diffraction lines of Table 1 of thisspecification in the absence of added binder.

It is a further object of the invention to provide a method forpreparing zeolites having the X-ray diffraction lines of Table I of thisspecification having a small crystallite size.

It is a further object of one embodiment of the invention to provide amethod for preparing zeolites having the X-ray diffraction lines ofTable 1 of this specification in commercially useful forms without anypost crystallization forming steps.

It is a further object of the invention to provide a method forpreparing zeolites having the X-ray diffraction lines of Table 1 of thisspecification at reduced raw material costs.

These and further objects and advantages, which will be apparent tothose skilled in the art, are realized in accordance with the presentinvention, wherein a crystalline zeolite having the X-ray diffractionlines of Table 1 of this specification is prepared by a method includingpreparing a template-free reaction mixture including at least one activesource of a first oxide selected from the group consisting of an oxideof silicon, germanium or both, optionally at least one active source ofa second oxide selected from the group consisting of an oxide ofaluminum, boron, gallium, iron or a mixture thereof; and heating thereaction mixture at crystallization conditions for sufficient time toform a crystallized material containing zeolite crystals having theX-ray diffraction lines of Table 1, wherein the zeolite crystals have afirst oxide/second oxide molar ratio greater than 12 and where theheating occurs in the absence of an added external liquid phase and/orthe reaction mixture has a molar ratio of H₂O/SiO₂ of less than about 8.

It is important, in preparing the reaction mixture of the presentprocess, that the amount of water present in the reaction mixture asprepared for the crystallization step be sufficient to shape themixture. While it is not a requirement to form the mixture into shapedparticles before the mixture is subjected to crystallization conditions,it may be desired in many cases to do so. This amount of water is lessthan the amount of water required in conventional processes forpreparing zeolites having the X-ray diffraction lines of Table 1 of thisspecification. Thus, during the crystallization step according to thisembodiment of the present process, there is no separate liquid phasepresent which must be removed from the crystallized material at the endof the crystallization step by, for example, filtering or decanting,prior to drying the crystals. Also, the amount of water present in thereaction mixture is insufficient to cause the shaped reaction mixture tocollapse or “melt”, i.e., once the reaction mixture is formed into thedesired shape containing the desired amount of water, the resultingshape is self-supporting.

Among other factors, one embodiment of the present invention is based onthe discovery of a method for crystallizing zeolites having the X-raydiffraction lines of Table 1 of this specification from a reactionmixture containing only enough water to form the mixture into a desiredshape, and another embodiment is based on the discovery of a method forcrystallizing zeolites having the X-ray diffraction lines of Table 1 ofthis specification from a template-free reaction mixture and a reactionmixture containing only enough water to form the mixture into a desiredshape.

IV. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A. Description of Zeolites

The method of making zeolites of the present invention includes a methodof making zeolites having the following X-ray diffraction pattern.

TABLE 1 Interplanar Spacing d (A) Relative Intensity 11.1  +/−0.3 S10.0  +/−0.3 S 7.4  +/−0.2 W 7.1  +/−0.2 W 6.3  +/−0.2 W 6.04 +/−0.2 W5.56 +/−0.1 W 5.01 +/−0.1 W 4.60 +/−0.08 W 4.25 +/−0.08 W 3.85 +/−0.07VS 3.71 +/−0.05 S 3.04 +/−0.03 W 2.99 +/−0.02 W 2.94 +/−0.02 W

These values were determined by standard technique. The radiation wasthe K-alpha doublet of copper, and a scintillation counter spectrometerwith a strip chart pen recorder was used. The peak heights, I, and thepositions as a function of 2 times theta, where theta is the Braggangle, were read from the spectrometer chart. From these, the relativeintensities, 100 I/I_(o), where I_(o) is the intensity of the strongestline or peak, and d (obs.), the interplanar spacing in A, correspondingto the recorded lines, were calculated. In Table I, the relativeintensities are given in terms of the symbols W=weak, S=strong andVS=very strong. It should be understood that this X-ray diffractionpattern is characteristic of all the species of ZSM-5 zeolites. Ionexchange of the sodium ion with cations reveals substantially the samepattern with some minor shifts in interplanar spacing and variation inrelative intensity. Other minor variations can occur depending on thesilicon to aluminum ratio of the particular sample, as well as if it hasbeen subjected to thermal treatment.

Zeolites having such X-ray diffraction pattern are typically designatedin the art as “ZSM-5 Zeolites”.

B. Reaction Mixture

Zeolite ZSM-5 and the conventional preparation thereof are described in,e.g., U.S. Pat. Nos. 3,702,886 and 3,770,614, the disclosures of whichare incorporated herein by reference in their entirety. ZSM-5 typezeolites can be suitably prepared from a substantially template-freereaction mixture containing sources of an alkali metal oxide, an oxideof aluminum, and preferably wherein the aluminum oxide source providesaluminum oxide which is in a covalently dispersed form on silica, and anoxide of silicon. The reaction mixture should have a composition interms of mole ratios falling within the following ranges:

TABLE 2 Broad Preferred More Preferred SiO₂/Al₂O₃  5-200  20-150  30-100OH⁻/SiO₂ 0.1-0.5  0.1-0.4 0.1-0.3 M⁺/SiO₂ 0.0-0.50 0.1-0.5 0.1-0.4H₂O/SiO₂ 2-8  3-7 3-6

wherein M is an alkali metal ion, preferably sodium or potassium, mostpreferably potassium.

Typical sources of aluminum oxide for the reaction mixture includealuminates, alumina, Al(OH)₃, and aluminum compounds, such asaluminum-coated colloids, Al₂(SO₄)₃, and other zeolites, withaluminates, e.g., Na aluminate, and aluminum hydroxide preferred.

Typical sources of silicon oxide include precipitated silica, silicates,silica hydrogel, silicic acid, colloidal silica, fumed silicas,tetraalkyl orthosilicates, and silicic hydroxides. Salts, particularlyalkali metal halides such as sodium chloride, can be added to or formedin the reaction mixture. They are disclosed in the literature as aidingthe crystallization of zeolites while preventing silica occlusion in thelattice.

The reaction mixture in the preparation of ZSM-5 is maintained at anelevated temperature until the crystals of the zeolite are formed. Thetemperatures during the hydrothermal crystallization step are typicallymaintained from about 100° C. to about 200° C., preferably from about100° C. to about 180° C., and most preferably from about 100° C. toabout 160° C. The crystallization period is typically greater than 1 dayand preferably from about 2 days to about 10 days.

The hydrothermal crystallization is conducted under pressure and usuallyin an autoclave so that the reaction mixture is subject to autogenouspressure.

C. In-Extrudate Aspects of the Reaction Mixture

To accomplish the in-extrudate crystallization, the substantiallytemplate-free reaction mixture from which and in which the zeolite iscrystallized comprises at least one active source of silica, andsufficient water to form the mixture into a desired shape. This amountof water is considerably less than that required in a conventionalprocesses for preparing zeolites. The H₂O/SiO₂ molar ratio in thereaction mixture is less than about 8 and preferably from about 3 toabout 6.

The amount of liquid required in the reaction mixture of the presentinvention, where the liquid may include aqueous and, optionally, organicliquids (i.e., excluding templates/structure-directing agents), is thatamount which is needed to adequately blend the mixture. Thus, a reactionmixture is prepared by mixing water with active sources of the zeoliteto form a uniform mass having preferably a heavy paste-like consistency.The active sources will be in a form which can be easily blended into auniform mass, and may be, for example, powders, hydrated particles, orconcentrated aqueous solutions. Sufficient water is added to wet all thepowders during the mixing and kneading steps.

Alternatively, sufficient water is added that the powders may be kneadedinto a uniform and generally homogeneous mixture which may be formedinto shaped particles. It is not necessary that all of the activesources be readily soluble in water during kneading, since the wateradded to the active sources will be insufficient to make a fluid-likemixture. The amount of water added depends on the mixing apparatus andon the active sources employed. Those familiar with the art can readilydetermine, without undue experimentation, the amount of liquid requiredto properly mix active sources of the zeolite. For example, hydratedsources of the zeolite may require relatively less water, and driedsources may require relatively more.

The water content of the reaction mixture after blending and kneadingmay be further adjusted, for example, by drying or the addition ofwater, to facilitate forming shaped particles.

Other metallic components which may be added to the reaction mixtureinclude, for example, titanium, chromium, germanium, gallium, iron,boron and alkali and alkaline earth metals.

Typical sources of silicon oxide (SiO₂) include silicates, silicahydrogel, silicic acid, colloidal silica, fumed silica, tetraalkylorthosilicates silica hydroxides, precipitated silica and clays. Typicalsources of aluminum oxide (Al₂O₃) when used in the reaction mixtureinclude aluminates, alumina, and aluminum compounds such as AlCl₃,Al₂(SO₄)₃, aluminum hydroxide (Al(OH₃)), kaolin clays, and otherzeolites, with aluminates, e.g., Na aluminate, and aluminum hydroxidepreferred. Titanium, chromium, germanium, gallium, iron, boron can beadded in forms corresponding to their aluminum and silicon counterparts.Salts, particularly alkali metal halides such as sodium chloride, can beadded to or formed in the reaction mixture. They are disclosed in theliterature as aiding the crystallization of zeolites while preventingsilica occlusion in the lattice.

The reaction mixture may also comprise one or more active sources ofalkali metal oxide. Sources of lithium and sodium are preferred, withsodium most preferred. Any alkali metal compound which is notdetrimental to the crystallization process are suitable here.Non-limiting examples include oxides, hydroxides, nitrates, sulfates,halogenides, oxalates, citrates and acetates. In the reaction mixture,the alkali metal/silica molar ratio is preferably in the range from zero(0) to about 0.5, and more preferably in the range from about 0.1 toabout 0.4. The alkali metal compound may also contribute OH⁻. Generally,zeolite synthesis is facilitated by the presence of OH⁻ in the reactionmixture at a molar ratio OH⁻/SiO₂ of about 0.1 to about 0.4, andpreferably from about 0.1 to about 0.3.

In the preferred method of the present zeolite synthesis, a reactionmixture is formed containing one or more sources of alkali metal oxide,hydroxide ions, an oxide of silicon, water, and optionally, an oxide ofaluminum. In general, the reaction mixture will have a pH of at least 7,and preferably between about 8and 14.

1. Seed Crystals

The zeolites of the present process are crystallized within the reactionmixture, which comprises amorphous, non-crystalline reagents.Crystalline material (i.e., “seed” crystals) are preferably added to themixture prior to the crystallization step, although ZSM-5 may becrystallized without the addition of seeds. Methods for enhancing thecrystallization of zeolites by adding “seed” crystals are well known.The broad range of seed crystals in the reaction mixture is greater thanabout 0 up to about 20 wt. % or more (based on dry weight), with thepreferred range at about 2-10 wt. %.

2. Forming the Shaped Particles

The In-Extrudate method may be used to make zeolite powder which canthen be bound by conventional methods using conventional binding agents.One advantage of the in-extrudate feature of the present invention isthat the reaction mixture may be formed into a desired shape before thecrystallization step, thereby reducing the number of process stepsrequired to prepare catalytic materials containing the zeolite preparedin the mixture. Prior to forming the reaction mixture, it may benecessary to change the liquid content of the reaction mixture, eitherby drying or by adding more liquid, in order to provide a formable masswhich retains its shape. In general, for most shaping methods, waterwill generally comprise from about 30 percent to about 65 percent byweight, and preferably from about 35 percent to about 60 percent byweight of the reaction mixture.

In the preforming step, the reaction mixture is formed into shapedparticles. Methods for preparing the particles are well known in theart, and include, for example, extrusion, spray drying, granulation,agglomerization and the like. The particles are preferably of a size andshape desired for the ultimate catalyst, and may be in the form of, forexample, extrudates, spheres, granules, agglomerates and prills. Theparticles will generally have a cross sectional diameter between about{fraction (1/64)} inch and about ½ inch, and preferably between about{fraction (1/32)} inch and about ¼ inch, i.e., the particles will be ofa size to be retained on a {fraction (1/64)} inch, and preferably on a{fraction (1/32)} inch, screen and will pass through a ½ inch, andpreferably through a ¼ inch, screen.

In the in-extrudate process of the present method, the shaped particlesprepared from the reaction mixture will contain sufficient water toretain a desired shape. Additional water is not required in the mixturein order to initiate or maintain crystallization within the shapedparticle. Indeed, it may be preferable to remove some of the excesswater from the shaped particles prior to crystallization. Conventionalmethods for drying wet solids can be used to dry the shaped particles,and may include, for example, drying in air or an inert gas such asnitrogen or helium at temperatures below about 200° C. and at pressuresfrom subatmospheric to about 5 atmospheres pressure.

Naturally occurring clays, e.g., bentonite, kaolin, montmorillonite,sepiolite and attapulgite, are not required, but may be included in theshaped particles prior to crystallization to provide particles havinggood crush strength. Such clays can be used in the raw state asoriginally mined or can be initially subjected to calcination, acidtreatment or chemical modification. Other reagents such as aluminas(e.g., Catapal, Versal), and which are mostly not incorporated into thezeolite structure, may also be added to improve extrudability orcatalyst physical properties. Microcrystalline cellulose has also beenfound to improve the physical properties of the particles.

3. Zeolite Crystallization

As stated above, the liquid present in the reaction mixture (which maybe in the form of shaped particles) may be a combination of aqueous andorganic liquids (i.e., excluding templates/structure-directing agents)so long as the specified amount of water is present. Since the totalliquid content may affect, for example, the physical strength of theshaped particles, it is preferred that the total volatiles content ofthe reaction mixture during crystallization be in the range of betweenabout 30% and about 65% (w/w), and preferably between about 35% andabout 60% (w/w), where the total volatiles content is the measure oftotal volatile liquid, including water, in the reaction mixture. It is afeature of the present process that no additional liquid beyond thatrequired to form the shaped particles is required for zeolitecrystallization within the particles.

Crystallization of the zeolite takes place in the absence of an externalliquid phase, i.e., in the absence of a liquid phase separate from thereaction mixture. In general, it is not detrimental to the presentprocess if some liquid water is present in contact with the reactionmixture or with the shaped particles during crystallization, and it canbe expected that some water may be on the surface of the shapedparticles during crystallization. However, it is an objective of thepresent invention to provide a method of crystallizing zeolite ZSM-5 insuch a way as to minimize the amount of water which must be treatedand/or discarded following crystallization. To that end, the presentmethod provides a zeolite synthesis method which requires no additionalwater for crystallization beyond a sufficient amount of liquid requiredto form the particles. Indeed, under certain conditions, liquid waterpresent during crystallization may alter the form of the shapedparticles, and, in extreme circumstances, may cause the shaped particlesto lose their integrity or to dissolve. Thus, the amount of liquidemployed during crystallization is dictated largely by the requirementsfor forming shaped particles from active sources of the crystallinezeolite.

Crystallization is conducted at an elevated temperature and usually inan autoclave so that the reaction mixture is subject to autogenouspressure until the crystals of zeolite are formed. The temperaturesduring the hydrothermal crystallization step are typically maintainedfrom about 100° C. to about 200° C., preferably from about 100° C. toabout 180° C., and more preferably from about 100° C. to about 160° C.

It is an important feature of the present process that thecrystallization of zeolites is frequently accelerated relative toconventional crystallization methods. Thus, the crystallization timerequired to form crystals will typically range from about 3 hours toabout 10 days, and more frequently from about 10 hours to about 4 days.Under certain circumstances, crystallization times of less than 48 hoursare required to prepare crystallized material of high crystallinity. Inthe present method, the crystallized material collected following thecrystallization step will typically comprise at least about 50 weightpercent crystals. Crystallized material containing at least about 80weight percent crystals, and even at least about 90 weight percentcrystals, may also be prepared using the present method.

Once the zeolite crystals have formed, the crystals preferably arewashed with acidic or basic solutions, e.g., dilute HNO₃ or KOH inwater, to remove amorphous inorganic material, especially SiO₂, whichwould otherwise block the zeolite pores. This wash is usually followedwith a water wash. After the water wash, the crystals are then dried,e.g., at 90° C. to 150° C. for from 8 to 24 hours. The drying step canbe performed at atmospheric or subatmospheric pressures.

D. Zeolite Crystallite Size

A benefit of some embodiments of the present process is the smallcrystallite size of zeolite crystals formed in the process. Typically,the zeolite crystals are less than 10 micron in diameter (i.e., medianlength, the longest dimension) as determined by Scanning ElectronMicroscopy. Since small crystals are desirable for certain catalyticapplications, crystallization conditions can be tailored to producezeolite crystals with diameters of less than 1.0 micron, preferably amedian length less than 0.5 micron, more preferably less than 0.3micron. The crystal size of the zeolite may be determined by, forexample, grinding the shaped particles to separate the individualcrystals. High resolution electron micrographs of the separated crystalscan then be prepared, after which the average size of individual zeolitecrystals can be determined by reference to calibrated length standards.An average crystal size may then be computed in various well-known ways.

For purposes of this disclosure, average crystal size will be defined asa number average. It is important to note that, for purposes of thisinvention, zeolite crystal size is distinguished from what somemanufacturers term “zeolite particle size”, the latter being the averagesize of all particles, including both individual crystals andpolycrystalline agglomerates, in the as-produced zeolite powder.

As stated above, typically, the zeolite crystals are less than 10 micronin diameter as determined by Scanning Electron Microscopy. Since smallcrystals are desirable for certain catalytic applications,crystallization conditions can be tailored by, for example, reducingcrystallization temperature, by increasing aluminum content in thereaction mixture, by reducing the hydroxide content in the reactionmixture, by increasing the seed concentration, and/or by reducing thewater content of the reaction mixture of the shaped particles prior tocrystallization, to produce preferred zeolite crystal diameters.Preferred synthesis conditions for forming crystals smaller than 1micron are as shown in Table 4 below:

TABLE 4 SiO₂/Al₂O₃  20-100 OH⁻/SiO₂ 0.1-0.4 M⁺/SiO₂ 0.1-0.4 H₂O/SiO₂ 3-6wt. % seed crystals  0-10

F. Zeolite Post-Treatment

A crystallized material containing crystals of zeolite is prepared inthe process as described above. The synthetic zeolite can be used assynthesized or can be thermally treated (calcined). Usually, it isdesirable to remove the alkali metal cation by ion exchange and replaceit with hydrogen, ammonium, or any desired metal ion. The zeolite can beleached with chelating agents, e.g., EDTA or dilute acid solutions, toincrease the silica:alumina mole ratio. These methods may also includethe use of (NH₄)₂SiF₆ or acidic ion-exchange resin treatment.

The zeolite can be used in intimate combination with hydrogenatingcomponents, such as tungsten, vanadium, molybdenum, rhenium, nickel,cobalt, chromium, manganese, or a noble metal, such as palladium orplatinum, for those applications in which ahydrogenation-dehydrogenation function is desired. Typical replacingcations can include metal cations, e.g., rare earth, Group IA, Group IIAand Group VIII metals, as well as their mixtures. Of the replacingmetallic cations, cations of metals such as rare earth, Mn, Ca, Mg, Zn,Ga, Cd, Pt, Pd, Ni, Co, Ti, Al, Sn, Fe and Co are particularlypreferred.

The hydrogen, ammonium, and metal components can be exchanged into thezeolite. The zeolite can also be impregnated with the metals, or themetals can be physically intimately admixed with the zeolite usingstandard methods known to the art. And, the metals can be occluded inthe crystal lattice by having the desired metals present as ions in thereaction mixture from which the zeolite is prepared.

Typical ion exchange techniques involve contacting the synthetic zeolitewith a solution containing a salt of the desired replacing cation orcations. Although a wide variety of salts can be employed, chlorides andother halides, nitrates, and sulfates are particularly preferred.Representative ion exchange techniques are disclosed in a wide varietyof patents including U.S. Pat. Nos. 3,140,249; 3,140,251; and 3,140,253.Ion exchange can take place either before or after the zeolite iscalcined. Following contact with the salt solution of the desiredreplacing cation, the zeolite is typically washed with water and driedat temperatures ranging from 65° C. to about 315° C.

After washing, the zeolite can be calcined in air or inert gas attemperatures ranging from about 200° C. to 820° C. for periods of timeranging from 1 to 48 hours, or more, to produce a catalytically activeproduct especially useful in hydrocarbon conversion processes.Regardless of the cations present in the synthesized form of thezeolite, the spatial arrangement of the atoms which form the basiccrystal lattice of the zeolite remains essentially unchanged. Theexchange of cations has little, if any, effect on the zeolite latticestructures.

The zeolites may be used as catalysts, without additional forming, whenthe shaped particles, formed from the reaction mixture describedhereinbefore, are of a size and shape desired for the ultimate catalyst.Alternatively, the zeolite can be composited with other materialsresistant to the temperatures and other conditions employed in organicconversion processes, using techniques such as spray drying, extrusion,and the like. Such matrix materials include active and inactivematerials and synthetic or naturally occurring zeolites as well asinorganic materials such as clays, silica and metal oxides. The lattermay occur naturally or may be in the form of gelatinous precipitates,sols, or gels, including mixtures of silica and metal oxides.

Use of an active material in conjunction with the synthetic zeolite,i.e., combined with it, tends to improve the conversion and selectivityof the catalyst in certain organic conversion processes. Inactivematerials can suitably serve as diluents to control the amount ofconversion in a given process so that products can be obtainedeconomically without using other means for controlling the rate ofreaction. Frequently, zeolite materials have been incorporated intonaturally occurring clays, e.g., bentonite and kaolin. These materials,i.e., clays, oxides, etc., function, in part, as binders for thecatalyst. It is desirable to provide a catalyst having good crushstrength, because in petroleum refining the catalyst is often subjectedto rough handling. This tends to break the catalyst down into powderswhich cause problems in processing.

Naturally occurring clays which can be composited with the syntheticzeolites of this invention include the montmorillonite and kaolinfamilies, which families include the sub-bentonites and kaolins commonlyknown as Dixie, McNamee, Georgia and Florida clays or others in whichthe main mineral constituent is halloysite, kaolinite, dickite, nacrite,or anauxite. Fibrous clays such as sepiolite and attapulgite can also beused as supports. Such clays can be used in the raw state as originallymined or can be initially subjected to calcination, acid treatment orchemical modification.

In addition to the foregoing materials, the zeolite prepared by thepresent method can be composited with porous matrix materials andmixtures of matrix materials such as silica, alumina, titania, magnesia,silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-beryllia, silica-titania, titania-zirconia as well as ternarycompositions such as silica-alumina-thoria, silica-alumina-zirconia,silica-alumina-magnesia and silica-magnesia-zirconia. The matrix can bein the form of a cogel.

The zeolite can also be composited with other zeolites such as syntheticand natural faujasites (e.g., X and Y), erionites, and mordenites. Theycan also be composited with purely synthetic zeolites such as those ofthe ZSM, EU, FU, and NU series. The combination of zeolites can also becomposited in a porous inorganic matrix.

Zeolites prepared in the present process are useful in hydrocarbonconversion reactions. Hydrocarbon conversion reactions are chemical andcatalytic processes in which carbon containing compounds are changed todifferent carbon containing compounds. Examples of hydrocarbonconversion reactions include catalytic dewaxing, catalytic cracking,hydrocracking, and olefin and aromatics formation reactions, includingformation from oxygenates. The catalysts are useful in other petroleumrefining and hydrocarbon conversion reactions such as isomerizingn-paraffins and naphthenes, polymerizing and oligomerizing olefinic oracetylinic compounds such as isobutylene and pentene-1, reforming,alkylating, isomerizing polyalkyl substituted aromatics (e.g., metaxylene), and disproportionating aromatics (e.g., toluene) to providemixture of benzene, xylenes and higher methylbenzenes.

V. ILLUSTRATIVE EMBODIMENTS

The invention will be further clarified by the following IllustrativeEmbodiments, which are intended to be purely exemplary of the invention.The results are shown below.

EXAMPLE 1

To 150 grams of silica (Hi-Sil 233, a hydrated silica manufactured byPPG) was added 5 grams of ZSM-5 seeds. To this was added 10 grams ofAI(OH)₃ (Reheis F2000, 53 wt. % Al₂O₃) plus 43 grams of a 50 wt. %aqueous solution of NaOH, and mixed for 20 minutes in a Baker-Perkinsmixer. To this was added 210 grams of water, with mixing continued foranother 20 minutes to form an extrudable paste. The mix was thenextruded through a {fraction (1/12)}-inch die on a Carver press. Molarratios in the extrudate were as follows:

SiO₂/Al₂O₃=43 OH-/SiO₂=0.24 Na⁺/SiO₂=0.24 H₂O/SiO₂=6.6

The extrudate was placed in a sealed Teflon bottle in a stainless steelpressure vessel and heated at autogenous pressure at 140° C. for twodays. The extrudate was washed with water brought up to pH 10.5 withNaOH, dried overnight in a vacuum oven at 120° C., and calcined in airfor 6 hours at 580° C. X-ray diffraction analysis showed the product toabout 60% ZSM-5 with no other crystalline phases.

EXAMPLE 2

To 150 grams of Hi-Sil 233 was added 5 grams of ZSM-5 seeds. To this wasadded 5 grams of Reheis F2000 plus 43 grams of a 50 wt. % aqueoussolution of NaOH, and mixed for 20 minutes in a Baker-Perkins mixer. Tothis was added 210 grams of water, with mixing continued for another 20minutes to form an extrudable paste. The mix was then extruded through a{fraction (1/12)}-inch die on a Carver press. Molar ratios in theextrudate were as follows:

SiO₂/Al₂O₃=86 OH-/SiO₂=0.24 Na⁺/SiO₂=0.24 H₂O/SiO₂=6.6

The extrudate was placed in a sealed Teflon bottle in a stainless steelpressure vessel and heated at autogenous pressure at 140° C. for twodays. The extrudate was washed with water brought up to pH 10.5 withNaOH, dried overnight in a vacuum oven at 120° C., and calcined in airfor 6 hours at 580° C. The yield, based on solids in the synthesismixture, was 65 wt. %. X-ray diffraction analysis showed the product toabout 100% ZSM-5 with no other crystalline phases. The average crystalsize was about 0.7 microns (by SEM).

What is claimed is:
 1. A method for preparing a crystalline zeolitehaving the X-ray diffraction lines of Table 1, said method comprising:(a) preparing a template-free reaction mixture comprising at least oneactive source of a first oxide selected from the group consisting of anoxide of silicon, germanium or both, optionally at least one activesource of a second oxide selected from the group consisting of an oxideof aluminum, boron, gallium, iron or a mixture thereof, and sufficientwater to shape said mixture; and (b) heating said reaction mixture atcrystallization conditions and in the absence of an added externalliquid phase for sufficient time to form a crystallized materialcontaining zeolite crystals having the X-ray diffraction lines of Table1, wherein said zeolite crystals have a first oxide/second oxide molarratio greater than
 12. 2. The method of claim 1, said method furthercomprising, after said preparing step (a) and before said heating step(b), forming said reaction mixture into shaped particles.
 3. The methodof claim 1: (a) wherein said first oxide comprises silicon and saidsecond oxide comprises aluminum; and (b) wherein the molar ratio ofSiO₂/Al₂O₃ in the reaction mixture is greater than
 50. 4. The method ofclaim 1, wherein said reaction mixture further comprises seeds of saidcrystalline zeolite.
 5. The method of claim 4, wherein said seedscomprise from about 1 wt. % to about 10 wt. % of the dry weight of saidreaction mixture.
 6. The method of claim 4, wherein said seeds comprisefrom about 1 wt. % to about 5 wt. % of the dry weight of said reactionmixture.
 7. The method of claim 1, wherein, in said heating step (b),said reaction mixture has a molar ratio of H₂O/SiO₂ of less than about8.
 8. The method of claim 7, wherein said molar ratio of H₂O/SiO₂ is atleast about 2 and not greater than about
 6. 9. The method of claim 1,wherein said zeolite crystals have a number average median length notgreater than about 0.5 microns.
 10. The method of claim 1, wherein saidzeolite crystals have a number average median length not greater thanabout 0.3 microns.
 11. A method for preparing a crystalline zeolitehaving the X-ray diffraction lines of Table 1, said method comprising:(a) preparing a template-free reaction mixture comprising at least oneactive source of a first oxide selected from the group consisting of anoxide of silicon, germanium or both, optionally at least one activesource of a second oxide selected from the group consisting of an oxideof aluminum, boron, gallium, iron or a mixture thereof, and sufficientwater to shape said mixture; and (b) heating said reaction mixture atcrystallization conditions, said reaction mixture having a molar ratioof H₂O/SiO₂ of less than about 8, for sufficient time to form acrystallized material containing zeolite crystals having the X-raydiffraction lines of Table 1, wherein said zeolite crystals have a firstoxide/second oxide molar ratio greater than
 12. 12. The method of claim11, wherein said molar ratio of H₂O/SiO₂ is at least about 2 and notgreater than about
 6. 13. The method of claim 11, said method furthercomprising, after said preparing step (a) and before said heating step(b), forming said reaction mixture into shaped particles.
 14. The methodof claim 11: (a) wherein said first oxide comprises silicon and saidsecond oxide comprises aluminum; and (b) wherein the molar ratio ofSiO₂/Al₂O₃ in the reaction mixture is greater than
 50. 15. The method ofclaim 11, wherein said reaction mixture further comprises seeds of saidcrystalline zeolite.
 16. The method of claim 15, wherein said seedscomprise from about 1 wt. % to about 10 wt. % of the dry weight of saidreaction mixture.
 17. The method of claim 15, wherein said seedscomprise from about 1 wt. % to about 5 wt. % of the dry weight of saidreaction mixture.
 18. The method of claim 11, wherein said zeolitecrystals have a number average median length not greater than about 0.5microns.
 19. The method of claim 11, wherein said zeolite crystals havea number average median length not greater than about 0.3 microns.